1. Field of the Invention
The present invention relates to a laser wavelength converting apparatus using an optical fiber type wavelength converter.
2. Description of the Related Art
FIGS. 1A and 1B illustrate conventional wavelength converting apparatuses in use.
Referring to the diagrams, a laser beam from a laser light source 1 reaches an optical fiber type wavelength converter 2 to cause Cerenkov radiation of a second harmonic of the laser beam. The Cerenkov radiation beam is collimated by a conical lens (axicon) 3, and the collimated beam is then put through an objective lens (not shown) to provide a beam spot.
The axicon in use has one surface 31 shaped in a convex cone and the other surface 32 formed normal to a laser optical axis 4, as shown in FIG. 1A, or has both surfaces shaped in a convex cone, as shown in FIG. 1B.
When the radiation angle of the second harmonics changes due to a possible variation in the core diameter of the fiber type wavelength converter, a change in refractive index caused by a change in temperature of a non-linear optical material filled in the core, etc., the collimation by the axicon lens becomes incomplete, undesirably resulting in deteriorated performance, such as reduction in the amount of the main lobe of a focused spot or increase in the diameter of the spot.